1. Technical Field of the Invention
The present invention relates generally to the communications field and, in particular, to a battery for use with a mobile phone in conjunction with a hearing aid device.
2. Description of Related Art
A "tele-coil" is an inductive device that is placed near a telephone speaker and used to couple audio signals from the speaker to a hearing aid. Essentially, a pick-up coil is placed into the magnetic field of the speaker. The audio signals induced in the coil are amplified and coupled to the speaker or transducer of the hearing aid. Consequently, the tele-coil facilitates the use of telephones by people who have hearing problems.
The Hearing Aid Compatibility Act of 1988 requires all fixed and mobile telephones to be hearing aid compatible. The Federal Communications Commission (FCC) has set forth these requirements in 47 C.F.R. .sctn. 68.316, which states that the axial magnetic field generated at a telephone speaker by a -10dBV signal at 1kHz should be greater than -22dBA/m. The radial magnetic field generated at the speaker should be greater than -27dBA/m. However, although these requirements may be appropriate for fixed telephones operating in a relatively noise-free environment, they are not suitable for those environments where there is substantial noise.
For example, a mobile telephone employed in the North American Personal Communications System (PCS) can transmit at full power (1/2W) and generate peak axial noise of about -16dBA/m. A standard speaker used in a PCS mobile phone generates an axial magnetic field of about -17dBA/m at 80dBSPL. Consequently, the noise generated by a PCS mobile phone speaker produces a substantial amount of interference in a hearing aid that uses a tele-coil, and the tele-coil user is unable to distinguish the audio signal from the speaker-generated noise.
A different problem encountered by tele-coil users is that newer mobile phones utilize piezoelectric speakers that do not generate a magnetic field. Consequently, a tele-coil cannot be used to couple the audio signal from the speaker in such a mobile phone.